Mold for sand casting varying thickness articles

Abstract

A permanent casting mold has its casting cavity coated with a sand liner of varying thickness. The liner is thicker where the cast article section is thinner and the liner is thinner where the cast article section is thicker so as to permit the thicker sections to cool faster while the thinner sections cool slower. The different thicknesses of the liner are correlated so that the respective sections of the article are sufficiently cooled at about the same time for removal of the article from the mold. The mold is a cope and drag-type flask mold whose casting cavity halves are oversized relative to the cast article. The sand liner is formed therein by temporarily positioning a pattern within the permanent casting cavity halves and sand filling the space between the pattern and cavity wall. The exterior surface of the pattern corresponds to the cast surface of the article. Thus, the thicknesses of the different portions of the liner are determined by the amount that the corresponding portions of the casting cavity are oversized. A vacuum system opening into the casting cavity, when the cope and drag are closed together for casting, enables rapid filling of the sand-lined cavity with molten metal, wherein the entire casting process, including cooling of the cast article for removal, is performed rapidly.

Having fully described an operative embodiment of this invention, I now claim: 
     
       1. A sand casting mold for casting molten metal articles of varying thicknesses, comprising: a permanent mold having a pre-formed casting cavity which is oversized relative to the desired finished external size and shape of the cast article;   a sand liner applied upon the wall of the casting cavity to provide an interior sand wall surface corresponding to the desired finished cast article surface;   said liner having varied thickness portions reversely correlated to the varied thickness sections of the cast article, that is, the liner portions being thicker where the article is thinner and vice-versa, with the liner thicknesses being pre-selected so that the different thickness article sections cool at different rates, i.e. with thicker sections cooling faster than the thinner sections, but with the liner thicknesses being correlated for sufficiently cooling all of the varied thickness sections of the cast article at about the same time to a temperature for removal of the article from the mold.   
     
     
       2. A sand casting mold as defined in claim 1, and said mold being formed as a cope and drag-type flask, with each of the cope and drag having a portion of the casting cavity and its interior sand liner. 
     
     
       3. A sand casting mold as defined in claim 2, and including small-size openings formed through the permanent mold and communicating with the interior of the mold cavity; and vacuum applying means external of the mold for applying a vacuum, through said small size openings, within the casting cavity during the time that the molten metal is cast.   
     
     
       4. A sand casting mold for casting molten metal articles which have integral thicker, cross-sectional portions and thinner, cross-sectional portions, comprising: 
     
     
       a permanent mold having a preformed cavity within which the molten metal is cast and solidified into the article; said cavity being oversized relative to the desired finished external size and shape of the cast article, with the wall defining the cavity being spaced a predetermined, varying distance away from the surface of the article cast within the cavity, that is, the wall being shaped and sized so that the distances between the wall areas that overlap the article thicker and thinner portions are correlated to be greater for the article thinner portions and lesser for the article thicker portions;   a sand liner applied against the wall of the casting cavity and forming an interior sand wall surface corresponding to the desired finished cast article surface and against which the molten metal is cast to form the cast article;   the thickness of the sand liner corresponding to the varying distance between the sand wall surface and the wall defining the cavity in the permanent mold, whereby the liner thickness varies reversely in accordance with the thickness of the article portions, so that the liner is thicker where the corresponding cast article portions are thinner and the liner is thinner where the corresponding cast article portions are thicker;   and with the distances between the permanent mold wall and the sand mold surfaces being predetermined for correlating the molten metal to cool at different rates at the different thickness portions of the article, that is, with the thicker portions cooling faster than the thinner portions, and with said distances, and therefore, said liner thicknesses, being correlated for sufficiently cooling the molten metal at all of the varied thickness portions of the cast article at about the same time to a temperature permitting removal of the cast article from the mold.   
     
     
       5. A sand casting mold as defined in claim 4, and including said mold being formed as a cope and drag type flask, with each of the cope and drag having a portion of the permanent mold, with its portion of the casting cavity, and a portion of the interior sand liner. 
     
     
       6. A sand casting mold as defined in claim 5, and wherein the distances between the permanent mold cavity wall and the samd wall surface change gradually along the areas of the mold overlapping portions of the cast article which gradually change in thickness, with the change in distance being the opposite to the change in the thickness of the overlapped portions of the article. 
     
     
       7. A sand casting mold as defined in claim 11, and including small size openings formed through the permanent mold and communicating with the interior of the mold cavity; and means for applying a vacuum, located externally of the mold, for applying a vacuum through said small size openings within the casting cavity during the time that the molten metal is cast.